DE69732832T2 - VIRTUAL TIME GRIND - Google Patents

Description

TECHNICAL TERRITORY

The The present invention relates to the field of clocking or synchronizing in a packet-switched network, especially in an ATM network.

BACKGROUND AND PRIOR ART

The Time calculation or synchronization of a digital transmission network is very important in most applications. It is essential that the transmission part and the receiving part of the transmission system use the same clock frequency and are in phase with each other. To achieve this, is for Most applications require some form of synchronization.

A An application that does not require synchronization is the ATM (asynchronous transfer mode) transmission network. However, need many devices or devices connected to an ATM network Form of synchronization, such as during a telephone conversation or a videoconference.

Of further may be the transmission network used also other transmission systems besides the ATM network, such as the public network Telephone Network (PSTN), which is often a synchronized network, for example, consisting of the Plesiochronous Digital Hierarchy (PDH) and Synchronous Digital Hierarchy (SDH) or synchronous digital Hierarchy. Therefore, the interface between the ATM network needs and the PSTN sync the regenerated or re-created provide generated user data passing through the ATM network be used.

Of the ATM standard specifies that the synchronization of the regenerated or re-generated user data from a synchronized source or transmit to a station either by the adaptive mechanism or the timestamp mechanism both are in the existing standard for the ATM adaptation layer be described for a circuit emulation (AAL1 in I363.1) can be used.

SUMMARY

It is an object of the present invention, a device and a To provide methods that are less complicated and cheaper Clock regeneration at the interface between a packet-switched Network, in particular an ATM network, and a synchronized Create a network.

These Task is solved by providing a clock signal directly at the interface from the synchronized network. Therefore, the sync remains receive. This will be solved by a method according to claim 1, and a receiving unit according to claim 5th

In In the present invention, the clock of a synchronized Master unit recovered by a slave unit, for example by means of the adaptive mechanism. The slave unit uses the recovered clock for transmission over the packet-switched network. Unpacking at the master page of the system is then executed using a clock signal that is provided directly from the synchronized network, the is called, without retrieving the clock by means of the adaptive mechanism or similar.

Therefore are received by the terminal unit, recovered data recovered by using the transfer clock Shut down the time loop at the interface to a synchronized Network when the user data over an asynchronous packet network transferred to a terminal unit and new data is returned in a synchronous manner retransmitted to the interface where synchronization and data are merged. there the method provides an interface to the synchronized network, the fully in agreement with existing synchronous interfaces by providing a network interface that closes the time loop locally and they merges with the user data from the external terminal unit.

SHORT DESCRIPTION THE DRAWINGS

The The present invention is accomplished by a non-limiting embodiment in terms of the accompanying drawings are described in more detail in which:

1 shows a block diagram illustrating a transmission path over an ATM network.

2a - b are schematic views of AAL units.

DETAILED DESCRIPTION

1 FIG. 12 is a block diagram illustrating a transmission path using an ATM network. FIG. In the diagram, a terminal unit wants 1 on a synchronized network 3 which may be, for example, the public switched telephone network (PSTN). The access path in this case consists of an ATM (Asynchronous transfer mode) network 5 ,

• – mittels des adaptiven Mechanismus.
• – mittels Zeitstempeln.

In this case, the terminal unit 1 assumed that it is a synchronized entity, such as a telephone. The terminal unit must therefore have access to a synchronization or a clock signal. This signal can be provided in two different ways according to the ATM standard for circuit emulation (AAL1 in I.363.1).

• - by means of the adaptive mechanism.
• - by means of time stamps.

Therefore, the duplex communication path passes between the terminal unit 1 and the synchronized network 3 from the synchronized network 3 who is the master of in 1 shown system, to an ATM adaptation layer (AAL) unit 7 in the from the synchronized network 3 originating data in ATM cells are packetized. In addition to the data, the AAL unit receives 7 a clock signal from the synchronized network 3 , The data will be on a data transmission line 9 delivered, and the clock signal is on a clock signal line 11 delivered. On her path from the synchronized network 3 to the AAL unit 7 the clock signal and the data signal exceed a G.703 interface 13 which is described in the appropriate standard.

The AAL unit 7 gives the ATM cells to the ATM network 5 which transfers the cells to the receiving end of the network, which in this example is the AAL unit 15 is. The AAL unit 15 unpacks the cells over the ATM network 5 Arrive. Furthermore, the AAL unit needs 15 Reproduce the data transfer rate to the terminal unit 1 with the synchronized network 3 to synchronize, which is the slave of the system. This is done by means of the adaptive mechanism, which does not need a separate transmission line to obtain the synchronization.

The through the AAL unit 15 unpacked data together with the re-generated (recovered) clock signal, are then on a data line 17 and a clock line 19 via a G.703 interface 21 to the terminal unit 1 transfer. Therefore, the terminal unit receives transmitted data and a synchronization signal.

When the terminal unit 1 Send data in the other direction, it transmits data on the data line 23 via the G.703 interface 21 to the AAL unit 25 , The terminal unit 1 will send its data using a clock that is fully synchronized with the incoming clock sent by the AAL unit 15 is provided by means of the adaptive mechanism. The outgoing clock will therefore be a mirrored representation of the synchronization received from the AAL unit 15 on the line 19 Will be received. The clock signal is sent via a clock line 27 transferred and also goes through the G.703 interface 21 , This method is fully consistent with existing synchronous mode units.

Then the ATM network transfers 5 the cells to the intended recipient, in this case the synchronized network 3 , At the receiving end there is an AAL 29 that is over the ATM network 5 unpacked to incoming cells. To synchronize the data contained in the incoming cells, the AAL 29 to access a synchronization signal. This signal can be obtained in the same manner as in the terminal unit end, that is, by means of the adaptive mechanism.

Since the terminal unit is a slave in the master / slave relationship between the synchronized network 3 and the terminal unit 1 is, but becomes the terminal unit 1 synchronized by the synchronized network. That's why the AAL 29 the synchronization or the clock signal provided by the AAL 7 , use. This is in the figure by the dashed line 31 shown.

This type of synchronization scheme is possible because the AAL unit 29 can assume that the timing or synchronization of incoming data from the terminal unit 1 the same as the timing of the data transmitted by the synchronized network. Therefore, the G.703 interface is not changed, but remains bidirectional. The AAL unit 29 can therefore data on a line 33 transmitted by the clock signal on the line 35 with the synchronized network 3 be synchronized.

In 2a the packetizing of the ATM cells is illustrated. The figure shows data on a wire 201 arrive and a clock signal on a line 203 arrives. The signals go through the G.703 interface 205 to a physical layer termination block 207 , In the block 207 The data is packetized into cells that become an ATM cell buffer 209 on the line 211 be transferred. The block 207 also sets the ATM cell buffer 209 with a clock signal on a line 213 ready. The ATM cell buffer 209 then gives the cells to the ATM network 215 at the correct times.

2 B provides de-packetization of ATM cells on the master side of the transmission system that is in 1 is shown, that is, at the synchronized network side. In 2 B cells come from the ATM network 221 at the ATM cell buffer 223 which buffers the incoming cells and defective incoming cells he puts up after. Furthermore, the buffer is depacketized 223 the cells, and the data contained in the cells, are sent to the synchronized network 225 via the G.703 interface 227 given.

To the data stream from the ATM cell buffer 223 To synchronize, a synchronization or a clock signal must be provided. A clock signal is therefore with the ATM cell buffer 223 connected, with the clock signal directly from the synchronized network 225 via the G.703 interface 227 on the line 229 comes.

The data is then sent to the synchronized network 225 in a synchronized manner via the data line 223 and the clock line 231 given.

Using the synchronization scheme described by way of example above, it will be possible to fully compensate for the large cell delay variation that is generated at an ATM or other packet-switched network, which is already in the AAL receiver 29 of the 1 takes place. This makes it possible to compensate for the phase difference that is maintained at this interface if the clock is newly generated by the adaptive mechanism.

By Providing the synchronization or the clock signal directly from the synchronized network to the ATM buffer, the time loop of the Simplified system. However, the scheme described above requires that the synchronization (clock) recovery at the slave end, the is called, the AAL at the terminal unit in the example given above, works as a malfunction same in too big Variations to handle on arrivals of cells for unpackaging ATM cell buffer at the master page of the system, where master synchronized Network in the example above.

Therefore a timing scheme has been described which simplifies the timing mechanism if an ATM network as an access network between two units configured in a master / slave relationship.

This is achieved with a system and method of simplification synchronization management in a system with a synchronized one Master and a slave unit, using a packet-switched network communicate, in particular an ATM network. The beat of a synchronized Master unit is recovered by the slave unit, for example by means of the adaptive mechanism. The slave unit uses the recovered clock to transmit over the clock packet-switched network. Unpacking at the master page of the system is then executed using a clock signal that is provided directly from the synchronized network, the is called, without recovering of the clock by means of the adaptive mechanism or the like.

Claims (8)

A method of using a derived Clock signal for synchronizing data received from a terminal unit be transmitted to a synchronized network, wherein the terminal unit to the synchronized network via a packet-switched network accesses and again one clock from the synchronized network generated when data over the packet-switched network from the synchronized network are received, characterized by the following steps: - Derive a clock signal directly from the synchronized network to a Receiving part located at an interface between the packet-switched Network and the synchronized network, - receive of data at the receiving part from the terminal unit via the packet-switched network and - Synchronize the received data at the receiving part based on the derived Clock signal. A method according to claim 1, wherein the packet-switched Network is an asynchronous transfer mode, ATM network. A method according to claim 2, wherein the receiving part is an ATM cell buffer in an ATM adaptation layer unit. A method according to any one of claims 1 to 3, wherein the synchronized network is a public telephone network PSTNist. A receiver located at an interface between a packet-switched network ( 5 ) and a synchronized network ( 3 ) and adapted to use a derived clock signal for synchronizing data received from a terminal unit ( 1 ) to the synchronized network ( 3 ) are transmitted when the terminal unit ( 1 ) to the synchronized network ( 3 ) via the packet-switched network ( 5 ) and reruns a clock from the synchronized network when data is transmitted over the packet-switched network (FIG. 5 ) from the synchronized network ( 3 ), characterized in that the receiving part for deriving a clock signal ( 31 . 229 ) directly from the synchronized network ( 3 ) is arranged to receive data from the terminal unit ( 1 ) over the packet-switched network plant ( 5 ) and for synchronizing the received data based on the derived clock signal ( 31 . 229 ). A receiving part according to claim 5, wherein the receiving part ( 29 ) at an interface between an asynchronous transfer mode ATM network ( 5 ) and a synchronized network ( 3 ) is located. A receiving part according to claim 6, wherein the receiving part ( 29 ) an ATM cell buffer ( 223 ) in an ATM adaptation layer unit ( 29 ). A receiving part according to any one of claims 5 to 7, wherein the receiving part is located at an interface between a packet-switched network ( 5 ) and a public telephone network, PSTN.